XBMC4Xbox

"if you mute XBMC then power off from menu, XBMC remembers that it was muted, but doesn't remember the previous volume value. therefore when you power on and unmute, it gets confused and sets to the minimum volume."
-Smiff

"the problem is that we only store the (current) volume not the mute state, so when it's muted during shutdown it will restore at minimum volume the next time when started. I think the best & easiest fix would be to restore to 0db in those cases, as you suggested. I don't see much in also storing the mute state...."
-Arnova

"this problem has been there at least 4 years. especially problematic when your remote volume keys are set to control something else (i.e. sound system) so user has no way to get sound back."
-Smiff

as discussed here
http://www.xbmc4xbox.org/forum/viewtopic.php?f=8&t=855